Functional element, in particular fluid pump, having a housing and a conveying element

ABSTRACT

The invention relates to a fluid pump ( 1 ) having a housing ( 5 ) delimiting a fluid chamber ( 13 ) and having a conveying element ( 8 ) for the fluid disposed in the fluid chamber, the housing ( 5 ), with respect to the shape and/or size thereof, being able to be changed between at least a first, expanded state and a second, compressed state. The object, to stabilise adequately a corresponding housing, is achieved according to the invention by the housing having at least one stabilisation chamber ( 19, 20, 25, 26, 31 ) which can be supplied with a fluid pressure and is different from the fluid chamber, the first state of the housing being assigned to a first fluid pressure in the stabilisation chamber and the second state of the housing being assigned to a second fluid pressure.

The present invention resides in the field of mechanical engineering, inparticular micromechanics, and can be used with functional elementswhich are used to convey or influence fluids.

The invention can be used particularly advantageously in medicaltechnology, where it is made to work, in particular in invasivemedicine, on body fluids, for example blood. For this purpose,micromechanical functional elements, for example pumps, are known, whichhave such a small construction that they can be conveyed through a bloodvessel. Pumps of this type can be operated within a blood vessel itselfor in a ventricle.

In order to enable a particularly efficient and effective operation, itis known to design such functional elements such that they have acompressed state in which they can be moved through a bloodstream andalso an expanded or dilated state which they can adopt for example afterintroduction into a ventricle or another body cavity. In this expandedstate, for example a pump can then have a rotor and a housing whichapply sufficient pump power by means of their size and nevertheless canbe introduced in the compressed state into the body and removed againtherefrom.

Various techniques are known for compressing or expanding such pumps.For example, so-called shape memory materials in the form of alloys areused, one of which is known by the trade name Nitinol, the correspondingcomponents generally adopting various geometric shapes as a function oftemperature. The type of construction can be designed such that a firstdimensional size is adopted in a first state of a Nitinol frame, whilsta second size is achieved in a second state at a different temperature.For example in the case of pumps, both the housings and the rotors canin principle be compressed and expanded in this way.

However pumps without rotors which transport a fluid by expulsion bymeans of volume changes are also known. Such a pump is known for examplefrom DE 10 2007 012 817 A1. Use of such a toroidal pump is known therefor assisting the heart, the pump being inserted in a blood vessel. Thehousing has a stable external shape but can be folded up. The whole pumpis designed as a double chamber hollow body, a balloon which can varywithin the housing effecting the volume change of a pump volume andhence suctioning in and expelling fluid. With respect to the type ofhousing and in addition in what manner this housing is compressible,nothing is stated in the document.

A pump is known from the public inspection document 4124299 A1, whichhas a housing which can be filled with a fluid and consequentlystiffened and also a conveying element which can be pumped up therein sothat alternately fluid in the housing interior can be suctioned in andexpelled.

Similar pumps are known from U.S. Pat. Nos. 5,820,542 and 5,827,171.

U.S. Pat. No. 5,928,132 discloses a pump with an expandable housingwhich can be stiffened by means of fluid-filled cavities.

Against the background of the state of the art, the object underlyingthe invention, in the case of a pump having a fluid chamber and ahousing delimiting the latter and also a conveying element disposed inthe fluid chamber, is to design the housing such that it can becompressed with respect to the radius and, on the other hand, can beexpanded and, in the expanded state, has as high stability as possible.

The object is achieved by the features of the invention according topatent claim 1.

In the case of a pump of the initially mentioned type, the housing, withrespect to the shape and/or size thereof, can be changed between atleast a first, expanded state and a second, compressed state, as aresult of the fact that it has at least one stabilisation chamber whichcan be supplied with a fluid pressure and is different from the fluidchamber, the first state of the housing being assigned to a first fluidpressure in the stabilisation chamber and the second state of thehousing to a second fluid pressure.

The different filling or pressure supply to the stabilisation chamberseffects different material stresses in the wall/the elastic walls of thehousing. For example, the stabilisation chamber or a plurality ofstabilisation chambers can be recessed on the housing walls, and thiswill typically lead to the fact that, at low pressure in thestabilisation chambers, the housing contracts elastically and relaxes,the housing walls become moveable and the housing diameter is reducedboth with respect to the outer diameter and with respect to the innerdiameter. For this purpose, at least the inner and/or the outer wall ofthe housing which directly surrounds the conveying element and, for itspart, is possibly surrounded by stabilisation chambers or onestabilisation chamber has an elastic configuration. In the case ofincreased pressure, the stabilisation chambers become taut and hence thewalls are for the moment widened and stiffened so that the housingexpands. The states can however also be chosen such that the walls ofthe housing have pre-tensions which lead to the fact that, in the caseof a high pressure application to the stabilisation chamber(s),compression of the housing is effected, whilst, at low pressure in thestabilisation chambers, expansion of the housing is effected due to theinherent stress of the housing walls.

It can thereby be advantageously provided that, in the second state, thediameter of the housing is reduced by the inherent elasticity to such anextent that the interaction element in its expanded state is compressedradially.

Hence, the elastic compression effect of the housing facilitates thecompression of the interaction element, for example a fluid conveyingelement. This can have for example the form of a pump rotor.

The cavity or cavities can be provided as recesses in a solid housingwall or as intermediate space/spaces between two spaced layers of thehousing wall—i.e. between an inner wall and an outer wall. Inner walland outer wall can have an equally elastic configuration or differentlyelastic configuration. The outer wall can thereby have a more flexibleconfiguration than the inner wall or the inner wall have a more flexibleconfiguration that the outer wall.

The elasticity of the housing wall in total is advantageous such thatthe housing contracts elastically and without folds from the expandedstate with a first inner diameter at least to half, in particular to athird, of the first diameter, when the inner pressure and also thepressure in the stiffening chambers is reduced. During compression, thehousing hence makes a decisive contribution to the compression of theconveying element, in particular of the rotor.

The housing wall can be designed for example as an open-pore foam, thepores on the inner and outer side of the wall being closed, e.g. bywelding or be a separate coating. If the expansion of the cavities isintended to take place by a material transport by diffusion or the like,then the open-pore foam can also be covered by a semipermeable membrane.

The structure of the cavities can also be such that a first group ofcavities is open towards one of the walls of the housing, e.g. in theform of access channels or as open-pore foam, and such that one or morecavities of a second group are embedded in the first group, respectivelyone semipermeable membrane being provided between the first and thesecond chambers. For example, the semipermeable membrane can surroundrespectively one or more cavities of the first group or of the secondgroup.

As partially permeable membrane for delimiting cavities, there can beused, according to the used filling materials for the cavities and thematerials which are intended to be allowed through or held back,membranes of microfiltration (0.5-0.1 μm particle size), ultrafiltration(0.1-0.01 μm particle size) and nanofiltration (1-10 nm). Independentlyof the particle size, basically biological or synthetic membranematerials can be used (as biological materials, for example Cuprophan,Hemophan or cellulose triacetate, as synthetic membrane for exampleTeflon or Goretex).

Synthetic materials in general have a higher water permeability and arethemselves often hydrophobic. There can be used as synthetic materials,polysylphone, polyamide, polyacrylonitrile and also copolymers thereofand also polymethylmethacrylates, polytetrafluoroethylene andderivatives thereof.

High-flux membranes are advantageously used, which allow throughmolecules up to a molecular weight of 50,000 Dalton and which ensurerapid material transport.

Advantageously, the material is chosen such that it retainsgerms/bacteria/microorganisms preventing contamination or infection.

Either a gas or a liquid, in particular a biocompatible liquid such assalt solution, can thereby be chosen as fluid for fillingcavities/stiffening chambers/stabilisation chambers. Advantageously, thehousing can have the shape of a hollow cylinder, a toroid or a hollowspheroid at least in portions. Such a shape basically leads to goodusability of the housing in a body since these shapes can basically bemoved easily through a naturally occurring body vessel. Arotational-symmetrical shape is possible in particular if the housing isused for a fluid pump. The housing is normally sealed at the ends,either by flat end-sides or by sealing surfaces which are conical orrotational-symmetrical in another way and have correspondinginflow/outflow openings.

The stabilisation chamber can be provided particularly efficiently inthe form of a cavity which is strand-shaped in the first housing state.In this case, the stabilisation chamber forms a stabilisation web as itwere in the housing wall in the case of high pressure application.Hence, a relatively small quantity of fluid is required in order to fillthe stabilisation chamber(s) and to stabilise the house. Advantageously,a plurality, in particular three or more stabilisation chambers, can beprovided in the form of strand-shaped cavities. These can be distributedsymmetrically in the housing.

It can also be provided advantageously that at least one strand-shapedcavity (viewed in the expanded state of the housing) has acircumferential configuration in the circumferential direction of thehollow cylinder, toroid or hollow spheroid. In this case, a particularlyefficient stabilisation structure for the housing is produced, whichcounteracts in particular a compression of the housing during pressureapplication to the stabilisation chamber. This is particularlyadvantageous when the functional element is designed as a fluid pump anda suction pressure is produced within the housing at least at times inorder to suction in body fluid, in particular blood. At this moment, thehousing is sensitive to the tendency to collapse and must in particularbe stabilised relative to this compression. Also a toroidal or hollowcylinder-shaped body can be provided as stabilisation chamber.

Alternatively or additionally to a strand-shaped cavity as stabilisationchamber, which extends in circumferential direction, one or morestrand-shaped cavities can extend parallel to the longitudinal axis ofthe hollow cylinder, toroid or hollow spheroid in the wall thereof. Inthis way, a stabilisation grating can be formed, which, at a low totalvolume of the stabilisation chambers, allows good stabilisation and agood, i.e. a high ratio, between the radius of the housing in theexpanded state and the radius in the compressed state.

It can also advantageously be provided that the stabilisation chamberessentially fills the space of the housing wall. As a result, thestructure of the housing is simplified and this can be filled or alsoemptied again rapidly and without complication by pressure application.The housing can then have for example the shape of a hollow-walledballoon.

In many case, it can be provided for stabilisation that thecorresponding cavities are penetrated by webs of the housing material.In this way, stabilisation of the housing even relative to a relativemovement of inner and outer walls is achieved.

On its housing, the fluid pump has an inflow opening and an outflowopening which can be provided respectively with a valve, in particular aone-way valve. It can be ensured in this way that the function isoptimised during use as a pulsating pump with a suction phase and anexpulsion phase. Body fluid is then suctioned in through the inflowopening, whilst this is conducted out through the outflow opening in theexpulsion phase.

Basically, such a housing can also be provided with a conveying elementwhich is designed as rotor with at least one blade for the fluid. It canthereby be provided that the conveying element is radially compressibleby folding in, folding up or collapsing the conveying blades.

The blade/blades can thereby be flexible elastically radially towardsthe rotor axis.

However, the rotor can also consist at least partially of avolume-compressible material, in particular a foam.

Additionally or alternatively to the housing, the rotor can likewisehave compressible cavities.

The rotor can thereby also be configured without a hub, the blade beingstabilised in a self-supporting manner as conveying surface andtransmitting the torque.

In connection with the present invention, the advantage of acompressible rotor resides in the fact that the latter is at leastpartially compressed already by the contraction of the housing so thatno high additional forces require to be applied when the fluid pump mustbe moved through a blood vessel in a body.

A further advantage of the elastic contraction of the housing resides inthe fact that the forces act regularly radially inwards on the rotor. Ifthe housing collapses when it is merely relaxed, then the effect on therotor is not reproducible.

Advantageously, it can also be provided that the conveying element isdesigned as a fluid-fillable hollow body/balloon which can hence bechanged with respect to its volume. Hence, it is achieved that expulsionin the interior/fluid chamber of the housing takes place with pressureapplication to the hollow body so that the fluid situated there isexpelled. If the pressure application to the hollow body is reduced,then the latter is compressed by the elasticity of its walls and freesadditional volume in the housing so that fluid from outside is suctionedinto the fluid chamber of the housing.

Hence a pulsating pump is produced for conveying the fluid.Advantageously, the conveying element in the filled form can essentiallyfill the fluid chamber of the housing. Hence, the stroke of the pump isoptimised when fluid is suctioned in and expelled.

Advantageously, the conveying element can be filled with the same fluidas the stabilisation chamber(s). Since both the stabilisation chamber(s)and the conveying element must be supplied with pressure afterintroduction of the functional element into the body, greatsimplification is produced if the same fluid can thereby be used.Normally, a biocompatible fluid, for example a salt solution, is used.However, also the use of a gas, for example a bioinert gas such ashelium, is conceivable.

Handling is further simplified by the conveying element and thestabilisation chambers of the housing being able to be connected to thesame fluid pressure source.

The object of the invention, to produce a fluid pump having acompressible housing, is also achieved by the following functionalelement. Involved hereby is a fluid pump having a housing delimiting afluid chamber and having a conveying element for the fluid disposed inthe fluid chamber, both the housing and the conveying element, withrespect to the shape and/or size thereof, being able to be changedbetween at least a first, expanded state and a second, compressed state,the average change in density of the housing material between the firstand the second state being at least 10%.

There is hereby meant the average change in density of the housingmaterial at constant temperature, for example 36° C. The local change indensity of the housing can vary greatly, what is crucial is the averagechange in density of the housing material, this housing material notrequiring at all to be homogeneous, but rather for example metallicparts can also be a component here which would then have acorrespondingly smaller change in density.

Preferably, reversibly or even irreversibly deformable materials shouldbe provided here, which, because of an osmotic mode of operation in thedecompressed state, have a greater volume/smaller density, or foamswhich have a smaller density in the decompressed state. These foams canbe open-pore or closed-pore.

The housing is preferably distinguished by a material mixture or amaterial which can be converted by compression from a first, lowerdensity or from a first, lower specific weight to a second, higherdensity or a higher specific weight. The cavities can thereby be closedand filled with a gas, such as for example air or nitrogen, or a noblegas or another bioinert gas which can be compressed easily in volume bypressure.

Such closed cavities tend to expand again in the absence of an externalpressure force due to the gas elasticity so that the housing, as soon asit is brought to the place of use, can unfold again automatically. Atleast the unfolding movement is assisted however by the gas elasticity.

In addition, also gas lines to the housing can however be provided,which gas lines end in one or more cavities and actively allow thecavities to be pumped up. The gas for the compression can possibly alsobe suctioned out via the same lines.

Likewise, the operation can take place with a liquid if this isintroduced into the cavities, if a liquid is situated in the cavities,then this is normally very much less compressible but, due to suitablechoice of the viscosity in cooperation with the remaining constructionalparts of the housing, it can enable high moveability and hencecompressibility nevertheless support a certain housing stability duringoperation due to the incompressibility after unfolding of the housing.

The cavities can also have an open design, hence high compressibilitylikewise being provided. The material which delimits the cavities mustthen have a correspondingly elastic configuration. This can be providedfor example in the case of an open-pore foam.

The invention can also be implemented advantageously by thecavity/cavities being at least partially delimited by a partiallypermeable membrane.

In this case, a cavity can be filled with a liquid which, together withthe membrane used and as a function of the liquid in which the pump canbe inserted, in particular human blood, allows diffusion into the cavityas a result of osmosis, which leads to an increase in pressure and topumping-up of the housing.

Likewise, also materials can be used which, after coming in contact withthe liquid to be conveyed, lead to swelling processes as a result ofabsorption of the liquid and hence assist decompression of the housingvia an increase in volume.

In the case of the osmosis process, filling the cavities with a salt ora salt solution, the salt concentration of which is higher than that ofthe liquids to be conveyed, is possible. For this purpose, alsosemipermeable membranes which surround fluid-filled stabilisationchambers at least partially and which can be designed as biological orsynthetic membranes, for example cellulose-based, are then provided.

Advantageously, it can also be provided that at least the predominantpart of the cavities is surrounded by solid material of the housing andconnected via openings to the outside and/or to each other. In thiscase, during compression, a fluid transport can take place via thecavities and possibly also out of the housing so that the correspondingcavities can be easily compressed entirely.

The housing can consist for example partially of a porous material, suchas foam, in particular polyurethane. Such a foam can be open- orclosed-pore. In the case of an open-pore foam, the elasticity is basedon the supporting material which surrounds the pores and moves aftercompression by itself back into its original form, the gas or fluidbeing able to flow back into the pores. Due to the limited flowcross-sections of the connections of the cavities/pores to each other, atime constant in the compression/decompression can be chosen withinspecific limits. This can ensure, during operation of the pump, thatsudden deformations of the housing due to irregular mechanical loadingare counteracted.

It can be provided to produce such a housing by injection of a foam intoa pre-manufactured mould.

The invention is shown in a drawing and subsequently described withreference to an embodiment in the following.

There are thereby shown

FIG. 1 an overview of the use of a fluid pump according to the inventionin a blood vessel,

FIG. 2 a longitudinal section through a fluid pump with a compressedconveying element,

FIG. 3 a longitudinal section as in FIG. 2 with an expanded conveyingelement,

FIG. 4 a longitudinal section through a housing with stabilisationchambers,

FIG. 5 a cross-section through the construction according to FIG. 4,

FIG. 6 a longitudinal section through a housing having a furtherconfiguration of stabilisation chambers,

FIG. 7 a cross-section as indicated in FIG. 6,

FIG. 8 a longitudinal section through a hollow balloon-like housing inspheroid form,

FIG. 9 a longitudinal section through the functional element in total incompressed form,

FIG. 10 a fluid pump in longitudinal section having a pump rotor,

FIG. 11 in a side view, a hub-free rotor and

FIG. 12 a detailed view of a pore structure.

FIG. 1 shows the functional element 1 in the form of a fluid pump in asection, inserted in the human body. The fluid pump is introduced bymeans of a hollow catheter 2 into a blood vessel 3 which leads to aventricle 4. The housing 5 of the fluid pump is connected to theinterior of the ventricle 4 via a suction hose 6 which extends throughthe blood vessel 3 and the suction hose there has one or more suctionopenings 7. The suction hose 6 is rounded off at its end in the vicinityof the suction openings 7 in order to avoid injuries to the interior ofthe heart.

Within the housing 5 of the fluid pump, a conveying element 8 in theform of a balloon is situated, in the present case essentially incylindrical form, which balloon is connected via a pressure line 9 to apressure source 10 outside the body. The pressure line 9 extends throughthe hollow catheter 2 and both are guided out of the blood vessel 3 tothe outside of the body in a lock, not represented.

The pressure source 10 is shown only schematically in the form of acylinder 11 and a piston 12 which is moveable therein, the pistonproducing, during a pulsating movement, a likewise pulsating pressurewhich leads to an alternating expansion and compression of the conveyingelement 8.

As a result, the conveying element 8 in the interior of the housing 5takes up more or less space alternately so that, as a countermove, moreor less space remains available for the fluid to be conveyed in thefluid chamber 13 of the housing 5. The fluid is hence expelled andsuctioned in by the conveying element 8 in a pulsating manner.

By using valve flaps, the fluid flow is directed in the desired form. Inthe illustrated example, valve flaps 14 are provided in the suction line6 and allow the fluid to flow in the direction of the arrow 15. Thevalve flaps could be provided equally well in the corresponding openingof the housing 5. Thereby involved is a return- or one-way valve whichallows the fluid to flow in the direction of the arrow 15 but not toflow out in the opposite direction. This leads to the fact that, duringcompression of the conveying element 8, fluid, i.e. in particular blood,can be suctioned via this path, but that this cannot flow out againthere during expansion of the conveying element.

Outflow flaps 16 which can be disposed for example directly on thehousing 5 and which likewise allow the fluid to flow out in only onedirection, namely in the direction of the arrow 17, are provided for theoutflow.

With cooperation of the valve flaps 14, 16, it is ensured that the fluidis conveyed from the fluid pump only in the direction of the arrows 15,17.

The throughput of the fluid pump is determined, apart from the residualpower of the patient's heart as long as this is still functioning, bythe pulsating frequency of the conveying element 8, on the one hand, andby the volume expelled respectively by the conveying element or by thefree volume remaining in the fluid chamber 13. The conveyance ismaximised when the conveying element can expand to completely fill thefluid chamber 13 and thereafter collapses so far that its interior iscompletely emptied. The conveying element can consist for this purposeof a highly elastic material which, after lowering the pressure in thepressure line 9, ensures compression of the conveying element. Thisleads to a pressure drop in the fluid chamber 13, as a result of whichfurther fluid is suctioned subsequently.

However, it is a prerequisite for functioning of this mechanism that thehousing 5 remains stable and does not collapse even when producing a lowpressure in its interior. This requirement is connected, according tothe invention, to the further requirement that the housing must becompressible for introduction and removal into and out of a body.

The invention provides for this purpose that the housing is providedwith at least one stabilisation chamber which stiffens the housing as aresult of pressure application.

In an extreme case, the entire housing can be configured thereby as adouble-walled balloon, the space between the balloon walls beingtypically at a higher pressure, in the expanded state, than the space ofthe blood vessel surrounding the housing. It can also be provided thatthis pressure is higher than the pressure prevailing at most in theconveying element and in the fluid chamber.

FIG. 2 shows schematically the state of a fluid pump having a hollowcylindrical housing 5 and a compressed conveying element 8 in thesuction phase. The fluid chamber 13 is essentially filled with the fluidflowing through the suction line 6.

The conveying element 8 has an essentially cylindrical form and consistsfor example of rubber or polyurethane or an elastomer with similarproperties, the surface of the conveying element being able to be coatedwith a material which, on the one hand, prevents infections and, on theother hand, avoids accumulation of blood on the surface. The samecoating can be provided in the interior of the housing 5 on the wallsthereof.

The conveying element 8 is connected to a pressure source via a pressureline 9 which is essentially designed not to be expandable.

FIG. 3 shows the configuration of FIG. 2 in an expanded state of theconveying element 8 in which the free residual space of the fluidchamber 13 is minimised and the fluid/the blood can flow out of openings18 of the housing 5 through valve flaps 16.

It should be noted than the housing 5 with respect to its outer diametercan be configured such that it does not completely fill the clearopening of the blood vessel 3 so that, when inserted into a body, bloodcan be conveyed through the vessel 3 by the inherent function of theheart, in addition to the fluid pump. However, it is also conceivablethat the diameter of the blood vessel is completely filled by a suitablychosen diameter also for specific purposes.

In FIG. 4, the strengthening of the housing 5 by stabilisation chambersis dealt with in more detail. In this embodiment, a plurality ofstrand-shaped stabilisation chambers 19, 20 is aligned parallel to thelongitudinal axis 21 of the housing 5 and disposed in We housing wall.

FIG. 5 shows a cross-section with seven such stabilisation chambers. Theindividual stabilisation chambers are separated from each other in thiscase and connected individually to a fluid pressure source via pressurelines 22, 23, 24. The stabilisation chambers can be supplied withpressure in order to stiffen the housing 5. In order to introduce orremove the housing 5, they are emptied so that the housing 5 cancollapse on itself.

The stabilisation chambers can also be connected amongst each other viaa pressure line in order to ensure that the same pressure respectivelyprevails in them and in order to simplify filling and emptying.

FIG. 6 shows another arrangement of the stabilisation chambers in theform of annular strands which are disposed respectively coaxially toeach other and to the housing 5. The stabilisation chambers aredesignated with 25, 26. In the embodiment, four of these stabilisationchambers are provided equidistant from each other in the housing wall.They are connected to a pressure source 29 by means of pressure lines27, 28.

Such annular or even possible, helical stabilisation chambers offerparticularly good stiffening of the housing and, during pressureapplication, a corresponding resistance to the pulsating low pressure inthe housing interior.

In the embodiment, the stabilisation chambers and the conveying element8 are connected to the same pressure source 29 via a multi-way controlvalve 30. As a result, the pressure source 29 can be used both forfilling the stabilisation chambers and for the pulsating pumping of theconveying element 8. FIG. 7 shows a cross-section through the housingrepresented in FIG. 6 in longitudinal section with a toroidalstabilisation chamber 26.

In FIG. 8, another concept of the housing within the scope of theinvention is represented, in which the housing wall is double-walled,the two outer walls (balloon walls) have a very thin design and thehousing is hence constructed in the manner of a balloon. The housingforms a double-walled balloon having a large cavity 31 which can howeverbe subdivided into a plurality of partial chambers. Either thinintermediate walls are provided for this purpose or, if no completesubdivision is desired, also only individual reinforcing struts in theform of webs 32, 33 can be provided. These ensure that inner wall andouter wall of the balloon cannot perform shear movements relative toeach other so that the housing 5 in total is stabilised. The interior 31is connected to the pressure source 29 by means of a pressure line 34.The housing 5 has in total the contour of a spheroid.

The stabilisation struts 32, 33 can typically consist of the samematerial as the balloon walls of the housing 5 and be produced in onepiece with the latter. The struts can thereby surround the housing 5annularly or be configured as axis-parallel webs. However, also anyorientation, for example even a grating-shaped structure, isconceivable.

Likewise, also in the above-described embodiments not only is theconcretely described orientation of the strand-shaped stabilisationschambers conceivable but also a grating-shaped or network-shapedstructure there which penetrates a solid housing wall.

In FIG. 9, finally the collapsed shape of the housing represented inFIG. 8 is shown, the spheroid being collapsed. The conveying element 8must likewise be compressed of course for introducing/removing the fluidpump into a blood vessel.

For removal of the fluid pump from the vessel, it can provided thatfirstly the housing 5 is collapsed by reducing the pressure in thestabilisation chambers and only thereafter is the conveying element 8emptied. As a result, an oblong shape is produced when the housing 5 isfolded up and the latter is predominantly prevented from collapsing inthe longitudinal direction and hence adopting a higher cross-section.The elastic contraction of the housing can thus also assist compressionof the conveying element.

By means of the invention, a functional element is formed which iscompressible to a high degree and nevertheless has the necessarystability in operation to resist both low and high pressures in adimensionally stable manner during pulsating pumping.

In FIG. 10, a housing 5 similar to that represented in FIG. 9 is shown,which however surrounds a pump rotor here, which rotates about itslongitudinal axis 40 and thereby conveys a fluid axially. The blades 41can thereby be secured individually to branch off on a shaft 42 or alsoa helically circumferential blade can be provided. The rotor is radiallycompressible and can be manufactured for example from a frameworkcomprising a memory alloy, for example Nitinol, or from another elasticmaterial. The rotor can have open or closed cavities in the bladesand/or the hub which are elastically compressible. In FIG. 10, the innerwall of the housing is designated with 46, the outer wall with 47. Atleast the inner wall can be widened and contracted elastically. Acontracted state of the housing 5 is represented in broken lines and theinner wall is designated with 43. This presses the blades 41′, in therepresented state, into a radially bent-in state so that the entirerotor is already reduced in size by some distance radially.

In FIG. 11, a hub-free rotor which can also be used is represented andconsists of a helically bent flat plate. This can consist for example ofan easily deformable or compressible material, such as for example asheet metal grating covered with foil or a foam, the rotor which isrepresented as open-pore or closed-pore is hub-free and self-supporting,i.e. the blade itself transmits the torque and is only mounted outsiderotatably and connected to a driveshaft 44 (FIG. 10) which extendsthrough a hollow catheter 45.

FIG. 12 shows, in greatly enlarged, microscopic representation, ahousing material in the form of a foam 132 having closed pores 128, 129,the material of the walls between the pores being configured, in avariant (cavity 128), as a semipermeable membrane.

Such a membrane allows the diffusion of specific liquids, which can beused for example for an osmotic effect. If the cavities/pores 128 arefilled for example with a liquid in which a salt in a highlyconcentrated form is dissolved and if the foam is brought into a liquidwhich has a lower solution concentration, then the combination tends tobring the concentrations of both liquids to approximate to each othersuch that the solvent diffuses from outside into the interior of thecavity 128 through the membrane 130. As a result, an increased osmoticpressure is produced and can be used to pump up the cavity 128 into theshape represented in broken lines. As a result, an expansion andstiffening of the foam can be achieved.

This effect can also be used specifically for larger cavities in thehousing. Alternatively, also swelling processes can be used to expandthe rotor.

In connection with the cavity 129, a hose 131 is represented andsymbolises that corresponding cavities can also be filled with a fluidvia individual or collective supply lines or that such a fluid can besuctioned out of them in order to control correspondingdecompression/compression processes.

1-21. (canceled)
 22. A fluid pump comprising: a catheter; a rotor; anexpandable housing defining an inner chamber configured to receive therotor, the housing configured to transition between a compressed stateand an expanded state within a blood vessel, the housing having anoutflow opening connected to the catheter and an inflow openingpositioned distal of the outflow opening, wherein an outer diameter ofthe housing is smaller than an inner diameter of the blood vessel whenthe housing is in the expanded state, wherein the housing comprises aninner wall and an outer wall, wherein the rotor is disposed within theinner chamber and configured to be radially compressed by the inner wallwhen the housing is in the compressed state; and a one-way inflow valvepositioned distal to the rotor.
 23. The fluid pump according to claim22, wherein the fluid pump further comprises an one-way outflow valvepositioned proximal of the inflow valve.
 24. The fluid pump according toclaim 23, configured such that, during operation of the pump, fluid issuctioned in through the inflow opening and out through the outflowopening.
 25. The fluid pump according to claim 23, wherein the outflowvalve comprises outflow valve flaps configured to prevent fluid flowfrom the catheter to the inner chamber.
 26. The fluid pump according toclaim 22, wherein the inflow valve comprises inflow valve flapsconfigured to prevent fluid flow from exiting the inner chamber in adirection distal to the inflow valve.
 27. The fluid pump according toclaim 22, wherein the housing comprises the inflow valve.
 28. The fluidpump according to claim 22, further comprising an elongate hosecomprising a proximal end and a distal end, the proximal end of theelongate hose connected to the inflow opening of the housing and thedistal end of the elongate hose configured to extend distally into aventricle of the patient.
 29. The fluid pump according to claim 28,wherein the elongate hose comprises the inflow valve.
 30. The fluid pumpaccording to claim 28, wherein the housing is configured to bepositioned within an aorta and a distal end of the elongate hose isconfigured to extend distally across the aortic valve.
 31. The fluidpump according to claim 22, wherein at least one of the inner and outerwall is configured to contract elastically from the expanded state intothe compressed state,
 32. The fluid pump according to claim 22, thefluid pump further comprising at least one expandable stabilizationchamber, wherein a change in inflation pressure of at least one of theinner chamber or the at least one expandable stabilization chambercorresponds to a transition between the compressed state and theexpanded state.
 33. The fluid pump according to claim 32, wherein the atleast one expandable stabilization chamber is disposed between the innerwall and the outer wall.
 34. The fluid pump according to claim 32,wherein the at least one expandable stabilization chamber is configuredto be supplied with a fluid pressure, wherein the compressed state ofthe housing corresponds to a first fluid pressure in the expandablestabilization chamber and the expanded state of the housingcorresponding to a second fluid pressure in the expandable stabilizationchamber, wherein the second fluid pressure is higher than the firstfluid pressure.
 35. The fluid pump according to claim 32, wherein the atleast one expandable stabilization chamber comprises an expandableregion, the expandable region having a distal end and a proximal end,and wherein a distal end of the rotor is positioned proximal to thedistal end of the expandable region when the housing is in thecompressed state.
 36. The fluid pump according to claim 22, wherein therotor comprises at least one blade, the blade being flexible elasticallyradially towards the rotor axis.
 37. The fluid pump according to claim36, wherein the rotor consists at least partially of avolume-compressible material.
 38. The fluid pump according to claim 32,wherein the rotor is designed to be hub-free.
 39. A fluid pumpcomprising: a catheter; a rotor; an expandable housing defining an innerchamber configured to receive the rotor, the housing configured totransition between a compressed state and an expanded state within ablood vessel, the housing having an outflow opening connected to thecatheter and an inflow opening positioned distal of the outflow opening,wherein an outer diameter of the housing is smaller than an innerdiameter of the blood vessel when the housing is in the expanded state,wherein the housing comprises an inner wall and an outer wall, whereinthe rotor is disposed within the inner chamber and configured to beradially compressed by the inner wall when the housing is in thecompressed state; and a one-way outflow valve positioned proximal to therotor.
 40. The fluid pump according to claim 39, wherein the outflowvalve comprises outflow valve flaps configured to prevent fluid flowfrom the catheter to the inner chamber.
 41. The fluid pump according toclaim 39, wherein the housing comprises the outflow valve.
 42. The fluidpump according to claim 39, further comprising an elongate hosecomprising a proximal end and a distal end, the proximal end of theelongate hose connected to the inflow opening of the housing and thedistal end of the elongate hose configured to extend distally into aventricle of the patient.